Microwave antennas and arrays thereof

ABSTRACT

1. In combination: a projectile having a nose portion with generally conical aerodynamic surface; a microwave antenna array situated in said nose portion and productive of a generally toroidal radiation pattern substantially coaxial with the longitudinal axis of said nose portion, said antenna array comprising a plurality of elongated grooves of substantially rectangular cross-section in said surface, said grooves lying substantially in planes common to said longitudinal axis of said nose portion and being spaced at intervals around said surface, each of said grooves being bounded by electrically conductive material; and means for feeding energy to said array through an aperture located at the bottom of each of said grooves and proximate one of the ends thereof.

United States Eatent [191 Hartley, Jr.

Sept. 2, 1975 MICROWAVE ANTENNAS AND ARRAYS THEREOF [75] Inventor: Harry F. Hartley, Jr., Oreland, Pa.

[73] Assignee: Philco-Ford Corporation, Blue Bell,

[22] Filed: Aug. 19, 1949 [21] Appl. No.: 111,123

[52] US. Cl. 343/708; 102/702 P; 343/771 [51] Int. Cl. H01Q 1/28 [58] Field of Search 250/33 SL; 102/702, 70.2 P; 343/705, 708, 770, 771, 789

[56] References Cited UNITED STATES PATENTS 2,403,567 7/1946 Wales, .lr, 102/702 P X 2,433,368 12/1947 Johnson.. 343/767 2,435,988 2/1948 Varian 343/771 X 2,487,622 11/1949 Wehner., 343/771 X Primary ExaminerMalcolm F. Hubler Assistant Examiner-Richard E. Berger Attorney, Agent, or Firm-Robert D. Sanborn EXENIPLARY CLAIM 1. In combination: a projectile having a nose portion with generally conical aerodynamic surface; a microwave antenna array situated in said nose portion and productive of a generally toroidal radiation pattern substantially coaxial with the longitudinal axis of said nose portion, said antenna array comprising a plurality of elongated grooves of substantially rectangular cross-section in said surface, said grooves lying substantially in planes common to saidlongitudinal axis of said nose portion and being spaced at intervals around said surface, each of said grooves being bounded by electrically conductive material; and means for feeding energy to said array through an aperture located at the bottom of each of said grooves and proximate one of the ends thereof.

3 Claims, 3 Drawing Figures PATENTEUSEP 21975 3.903.523

sum 1 BF 2 INVENTOR. Amer ,e A/mn; J/:

PATENTEDSEP 21975 sum 2 0f 2 1N VEN TOR. HARRY 1. 1934/9725) fi/K MICROWAVE ANTENNAS AND ARRAYS THEREOF The present invention relates to antenna apparatus for the propagation and reception of microwave energy. More specifically it relates to a novel microwave antenna structure especially adapted for use in airborne equipment under circumstances which impose stringent limitations upon the electrical as well as the mechanical characteristics of such an antenna.

Although, as will become clear from the subsequent discussion, apparatus in accordance with my invention may find employment under a variety of circumstances, it is primarily toward the application hereinbefore referred to that this discussion is directed.

From the electrical point of view it is frequently desirable to impart pronounced directional characteristics to a microwave antenna. Two important objectives are attained by so doing. First, by concentrating the major portion of the energy radiated by the antenna in some particular desired direction or sector, the total energy which the antenna need radiate, to obtain satisfactory transmission power levels, is decreased from the value required by an omnidirectional antenna, thereby reducing the power requirements of the transmitter which drives the antenna and, with it, the physical size and weight of the over-all installation. Secondly, regions lying outside of the directional characteristic will be unaffected by the radiation. Of the latter, the converse is also true that is, regions outside the directional characteristic will also be substantially incapable of affecting the radiation, thus reducing the amount of interference to which this radiation is subjected. It is consequently desirable to impart directional characteristics to a microwave antenna whenever other requirements permit, since a substantial saving in power and an attendant saving of Weight and cost of the installation may thereby be effected.

One situation, in which it is highly desirable from every point of view that the microwave antenna have a directional characteristic, arises when it is used in connection with the recently developed proximity fuse. The principle of operation of such a device is well known, and requires only short recapitulation here. Briefly, a small microwave transmitter, mounted in some type of explosive missile, sends out waves which are reflected from potential targets. A small receiver, which is also located in the missile, is capable of responding to certain of these reflected waves in such a manner as to detonate the explosive charge of the missile. In such a device, practically every requirement points toward the use of a directional antenna, in connection with the transmitter as well as with the receiver. To begin with, it is desirable that only targets within the fragmentation pattern of the missile be capable of detonating it. This. of course, immediately suggests the use ofa directional antenna, since such a device is the simplest means of rendering the receiver insensitive to reflections of waves from other objects. In addition, use of an antenna which is highly directional makes it very difficult to jam the receiver associated therewith, since jamming signals, in order to be effective, must not only be inherently capable of affecting the receiver, but must, in addition, arrive at the antenna from predetermined directions.

Evidently, the most effective missile is the one which carries the largest explosive charge in proportion to its total weight, all other performance factors being equal.

Hence it is desirable to reduce the weight of the transmitter and receiver to its lowest practical value. Since a certain minimum power must be radiated in order that targets may reflect an amount sufficient to actuate the receiver, the total power, and consequently the total weight of both, may be kept to a minimum by concentrating all of the energy in a given direction instead of permitting it to radiate freely in all directions. Thus, the antenna must needs be directional. Just what sort of directional pattern it should possess, on the other hand, depends on some other factors, such as its location within the confines of the missile, its operating range, the fragmentation pattern of the explosive charge and the like. Some of these factors and their influence on an antenna constructed in accordance with my invention, are discussed in more detail hereinafter.

Before going into these more detailed electrical features, however, it will be useful to examine some of the mechanical characteristics which this type of antenna must exhibit. Above all, its aerodynamic characteristics must be good that is, it must cause as little additional air resistance to the progress of the missile as possible. It must cause little, if any, turbulence which might alter the missiles desired path, and it must, in the case of a guided missile, cause no interference with the proper operation of the guiding controls or with their influence on the path of the missile. In addition, it must be of rugged construction in order to be able to withstand the high accelerations to which the missile may be subjected, and it must be simple and inexpensive enough to be expendable.

Although some antennas have been constructed in the past which exhibited most of the desired electrical characteristics and some others which were mechanically adequate, it was thought, heretofore, that the electrical and mechanical characteristics were so irreconcilable as to be incapable of simultaneous incorporation into a single structure. For example, the properly directional antennas required bulky parabolic reflector discs, or delicate dipoles, while the mechanically satisfactory antennas may have had substantially uncontrollable directional patterns. My novel microwave antenna fills this lacuna in the art by providing a structure which combines the desired electrical and mechanical characteristics as hereinbefore described.

It is, accordingly, a primary object of my invention to provide microwave antenna apparatus suitable for application to rapidly moving missiles and the like.

It is another object of my invention to provide a microwave antenna having easily determinable directional characteristics.

It is still another object of my invention to provide a microwave antenna capable of being mounted flush with the external surface of its supporting structure.

Yet another object of my invention is to provide a microwave antenna for explosive missiles which produces substantially no interference with the motion of such missiles.

These and other objects of my invention will become evident from the subsequent discussion as examined in the light of the accompanying drawings, wherein:

FIG. 1 is a diagrammatic representation of an explosive missile which will be useful in explaining some of the features of apparatus constructed in accordance with the invention;

FIG. 2 is a detailed and enlarged view of an antenna embodying the principles of my invention; and

FIG. 3, is an enlarged view of'the nose section of the missile pictured in FIG. I incorporating an embodiment of the invention.

Referring now to FIG. I, there is shown a typical embodiment of an explosive missile incorporating a proximity fuse. It is with the aid of this figure that the relationships between missile performance and antenna pattern are hereinafter discussed. For the sake of simplicity of exposition, and because those features which are relevant to my invention are subsequently more fully treated, only the principal components of such a missile are here illustrated. These are all enclosed within a hull which may be of some aerodynamically suitable shape, having, for example, a pointed nose section 13. Typically the space designated 11 may be occupied by the explosive charge. that designated 12 by a suitable transceiver, that designated 14 by the detonating apparatus, and that designated 15 by the fuel container and propulsion apparatus. The usual stabilizing and guiding surfaces 16 may be affixed to the missile in the manner shown and may be adapted for fixed adjustment prior to launching or, in certain instances, for control during flight by automatic mechanisms within the missile or by radio remote control from the ground or from aircraft.

Since only the antenna system, to which the trans ceiver 12 is coupled, is constructed in accordance with my inventive concept, and since the other components are quite conventional and readily interchangeable with a variety of specific forms, the latter will be treated herein only from the point of view of their overall performance and their bearing on the antenna system constructed according to my invention, In normal operation the missile is either aimed in the general direction of probable targets before launching, or is controlled while in flight, in the manner above referred to, to direct it into a region where targets exist. The transceiver is caused to commence operating either in response to the launching shock or, after a predetermined interval, in response to a preset timing device. The operation of the transceiver may be similar to that of a conventional radar set, in that the transmitter portion thereof generates pulses which are radiated during intervals when the associated receiver portion, which is connected to the same radiator as the transmitter portion, has been rendered insensitive. During the intervals between pulses, the receiver portion is sensitive, thereby placing it in condition to detect reflections of the radiated transmitter pulses. When the missile approaches a target sufficiently closely so that the target comes within the range of the antenna pattern of the missile, the receiver portion of the transceiver will detect the reflections of transmitted pulses from the target and may be caused to actuate the detonator to explode the missile.

It is clear that, if the antenna pattern of the missile coincides substantially with its fragmentation pattern, the operation hereinbefore described will result in damage to the target comparable to that which would result from a direct hit. Some effort at approximating this operation had previously been made by the use of time fuses which would cause the missile to explode either on impact or at a predetermined time after launching, whichever was first. However, in attempting to apply this technique against small, fast moving targets, such as missiles moving at velocities many times that of sound, and even rapidly moving aircraft, the difficulties of estimating altitude and time of flight to the target, and of actually aiming the missile, proved to be such as to make the likelihood of success about as small as that of scoring a direct hit. With a missile which exhibits the type of operation hereinbefore described, all the time and attention available at its launching may evidently be devoted to proper aiming, while the operation of the fuse insures that even a near miss will not result in the target remaining unscathed, provided the above men tioned relation between antenna pattern and fragmentation pattern prevails.

In general, the explosive charge of a missile of the type under discussion has an inherent fragmentation pattern which is directed radially outward with respect to the longitudinal axis of the missile. Since it is exceedingly difficult to ascertain, even in a guided missile, on which side of the missile the target will appear, the pattern is, furthermore, almost invariably omnidirectional in azimuth, where azimuthal direction is measured in a plane perpendicular to the longitudinal axis of the missile and from a point located at the intersection of the plane and the axis. In other words, the normal radial distance from the longitudinal axis over which the effect of the explosion is appreciable is substantially equal in all directions. Although this inherent fragmentation pattern of the missile contains little or no forward or backward component, such a forward component is effectively added thereto by the forward velocity of the missile at the point of explosion. Thus, the actual fragmentation pattern of a typical missile of the type under consideration, while still omnidirectional in azimuth, will be inclined forward in the direction of flight of the missile to an extent which depends on the relationship between the velocity of the explosion and the velocity of flight at the point of explosion. The faster the missile travels, the greater will be the forward inclination of the fragmentation pattern, other factors remaining equal.

Thus, if the requirement of coincidence between antenna pattern and fragmentation pattern is to be met, an antenna system for use in cooperation with a missile of this type must exhibit a pattern which is also omnidirectional in azimuth and inclined forward in the direction of flight of the missile. An elevational section through a typical antenna pattern of this type is represented in FIG. 1 by lobes 17 and 18 which represent graphically the relationship between field strength and angle of elevation, the increasing direction of field strength being radially outward from the respective virtual sources of radiation from which these lobes appear to emanate. This section is coplanar with the longitudinal axis of the missile, and since the pattern must be substantially uniform in azimuth in order to conform to the configuration of the fragmentation pattern, as hereinbefore described, the complete radiation pattern of the antenna system is of roughly toroidal shape, as formed by rotation of either of the lobes shown in FIG. 1 about the longitudinal axis of the missile. It is evident that, the missile being of metallic construction, the virtual sources of radiation represented in this sectional view at points 19 and 20, respectively, can, at best, be located in the outer surface of the missile as shown.

Thus the virtual source of the complete pattern will also be on the surface of the missile and will, in fact, lie along the circle formed by rotating either of points 19 and 2t) aximuthally about the longitudinal missile axis.

In discussing applicants invention hereinafter, it will be convenient to refer to the elevation of the antenna pattern, as above described, which may be defined as the angle a formed between the line drawn from the virtual source (eg 19) ofa typical lobe (e.g. l7) and the point (e.g. point A) on said lobe corresponding to maximum field strength, and a line drawn through said virtual source tangent to the surface of the missile nose at that point and lying in the plane of section of the lobe.

I have found that the required radiation pattern, as above defined, may be produced by employing an antenna array comprising a plurality of elongated grooves of substantially rectangular cross-section formed in the missile nose, said grooves lying substantially in planes common to the longitudinal axis of said surface and being spaced at intervals around said surface, and each .of said grooves being bounded by electrically conductive material. These radiating elements may conveniently be fed with electromagnetic wave energy, in accordance with my invention, through apertures in their bottoms, which are readily accessible from the inside of the missile. Moreover, the grooves may be filled with suitable dielectric material, the outer surfaces of which may be made to conform substantially to the contour of the aerodynamic surface of the missile nose so as not adversely to affect the aerodynamic properties of said surface. It has been found that, for most purposes, four radiating grooves of the sort described above, arranged at equal intervals around the nose surface of a missile, are sufficient to provide a satisfactory antenna pattern. The arrangement of such an array is illustrated in FIG. 3 of the drawings. However, before considering the manner of cooperation of the several radiating grooves to produce the desired over-all antenna pattern, it will be in order, first, to consider the detailed structure of a single radiating groove in accordance with the invention. The details of such an element are clearly shown in FIG. 2 of the drawings.

As illustrated, the radiating element comprises essentially an electrically conductive member 21, which may be of any suitable metal such as aluminum or copper, in which is formed an elongated groove 22 of substantially rectangular cross-section. Near one end of the groove, and in the side thereof opposite its open side, is a substantially rectangular aperture 23 through which electromagnetic wave energy may be supplied to the groove for radiation from the open side thereof. The result to be achieved in supplying energy to the groove is to cause electromagnetic waves to be propagated lengthwise in the groove from the end thereof at which aperture 23 is located to the opposite end, and to cause portions of the energy contained in said wave to be radiated outward through the open side of the groove at successive points throughout the length of the groove. To this end, the energy supplied to the groove through aperture 23 should have its electric field vector orientated in a direction normal to the sides of the groove. This objective may be achieved by supplying energy to the groove via aperture 23 by means ofa standard rectangular waveguide section 24 having its lesser cross-sectional dimension orientated perpendicular to the vertical side of the groove, However, for reasons which will be set forth more fully hereinafter, the width of the radiating groove will generally be substantially less than the lesser cross-sectional dimension of a rectangular wave-guide of the conventional type used to transmit energy of the frequency which the groove is designed to radiate. This necessitates the inclusion, between the end of the waveguide section 24 and the aperture 23, of a transition section 25, which at one end has a cross-section substantially conforming to the aperture 23 and, at the other end, a cross-section substantially conforming to that of the rectangular waveguide section 24. To insure proper and efficient transfer of energy from the waveguide section 24, via aperture 23, into the radiating groove 22, the crosssection of said transition section should vary gradually along the length thereof between said two ends. For example, it has been found that satisfactory results will usually be obtained if the length of the transition section is of the order of a Wavelength.

Since, for purposes of convenience and to avoid interfering with the aerodynamic properties of the surface in which the radiating element is to be employed, it is desired to supply energy to the radiating groove through an aperture in its bottom, certain other difficulties are introduced, for which, however, a solution is provided by the present invention. More specifically, energy thus delivered to the radiating groove through the aperture 23 in its bottom would normally tend to pass directly through the groove in a direction transverse to its longitudinal axis so as to cause substantially all of the energy thus supplied to be radiated through the open side of the groove, and substantially none of it to be propagated lengthwise down the groove. In accordance with the invention, this difficulty is overcome by providing a conductive barrier 26 extending across a fraction of the region of the open side of the groove which lies directly opposite the rectangular aperture 23. Such a conductive barrier may, for example, comprise a thin strip of metal 27 slidably supported by the side walls of groove 22 and of length less than that of aperture 23. It has been found that it is of considerable importance that this strip should make positive contact with the inner longitudinal edges of groove 22, since failure to achieve such intimate contact may produce undesired wave propagation effects which interfere with the formation of the desired antenna pattern. To this end, the central portion of strip 27 is longitudinally depressed, this depressed portion extending correspondingly into groove 22. The edges of the strip are firmly held down against the walls of the groove by retaining screws 28 and 29, thus achieving the positive contact hereinbefore specified. It has been found that the slight extension of the depressed portion into the groove does not interfere with the proper radiation of energy therefrom. The region longitudinally closed by this barrier may be adjusted by manually sliding strip 27 back and forth over the groove, screws 28 and 29 serving to clamp the strip securely in any desired longitudinal postion. Since the strip may extend adjustably beyond the narrow end of the groove, a depression is provided in the end wall of the groove so shaped as to conform to the depressed portion of the strip which slidably engages this depression. Fortunately, it has been determined that the intimacy of contact between the barrier and the transverse groove edge along the closed end of the groove is not particularly critical from the point of view of the antenna pattern so that no special precautions need be taken to insure positive contact there. The arrangement hereinbefore described therefore provides contact between the barrier and the slot end which is sufficiently close for all practical purposes. This conductive barrier functions to direct substantially all of the energy introduced through aperture 23 in a direction lengthwise down the groove. However, by reason of the fact that the conductive barrier does not extend across the entire region of the open side of the groove lying directly opposite the aperture 23, strong reflections are not introduced such as would tend drastically to affect the efficiency of supply of energy to the groove through aperture 23. The production of reflections by the barrier 26 and by the mismatch introduced by the presence of aperture 23 may be further minimized by appropriate adjustment of a matching screw 30 in the tapered wall of the transition section 25. The appropriate size of the barrier 26, and the appropriate adjustment of the matching screw 30, will vary depending upon the various paramters of the over-all antenna arrangement and can best be fixed, in a given instance, by experimentation.

The specific values of length, depth and width of the radiating groove 22 are important factors in determining the significant characteristics of the radiation pattern thereof, as will now be discussed. As shown in FIG. I, and also in FIG. 2, the radiation pattern, which it is desired to produce, comprises but a single lobe in elevation, it being recalled that the angle or of elevation is measured in a plane passing through the longitudinal axis of the radiating groove and with reference to a line parallel to said longitudinal axis and passing through the virtual source of the radiation. Prior experience has shown that the pattern may be restricted to a single lobe in elevation if the radiating groove is fed with energy from one end thereof, in the manner hereinbefore described, and if, further. the depth d of the groove is made to have a value between one-quarter and onehalf wavelength of the energy to be radiated. Under these conditions, energy will be propagated lengthwise in the groove 22 only in the lowest possible mode, and this will cause the radiation of but a single lobe.

As also discussed hereinbefore, and as illustrated in FIGS. 1 and 2, it is usually desirable that the angle of elevation 01 of the beam pattern should be somewhat less than 90, in order that the pattern may coincide with the fragmentation pattern of the moving missile. The depth d of the radiating groove is of further signifi cance in controlling this angle of elevation. It may be shown that if the groove is excited exponentially along its longitudinal axis this angle of elevation is related to the wavelength of the radiated energy roughly in the manner expressed by the formula:

( l where a is the angle of elevation of the entire radiation pattern of groove 22, A is the wavelength in free space of the energy radiated therefrom and A is the wavelength of the same energy while still in the groove. It may further be shown that A is related to the depth d of the groove in accordance with the expression:

nP-n where 6,, and ,u are respectively the dielectric constant and the electric permeability for free space, and e and ,u. are respectively the same constants for the material with which the groove is filled. Then, by substitution,

cos a (A /4d) (3) Thus it will be seen that, by selecting the value of d in accordance with this relationship and within the limits of one-quarter and one-half wavelength of the energy to be radiated, the antenna radiation pattern may be made to have almost any desired elevation.

Next it will be observed that the width w of the groove 22 and its length It cooperate jointly to determine the elevational width B of the antenna beam pattern, as indicated in FIG. 2. If the groove is made relatively wide, all of the energy supplied thereto through the aperture 23 will be radiated through the open side of the groove before it has had an opportunity to propagate any appreciable distance down the groove. This will have the effect of producing a beam of relatively wide elevational width B. On the other hand. by decreasing the width of the groove, the energy supplied thereto through aperture 23 may be caused to traverse a substantial length in the groove before all of it has been radiated through the open side. Then only a small fraction of the total energy supplied to the groove will be radiated through its open side within any small fraction of the length of the groove, and the result will be to produce a beam of relatively narrow elevational width. If circumstances permit, the length of the groove should be made just sufficient to provide the required beam width, and the width of the groove should then be selected so that not all of the supplied energy will have been radiated before at least a small fraction of the energy reaches the remote end of the groove. On the other hand, it is desirable so to select the width of the groove that substantially all of the supplied energy will have been radiated through the open side of the groove in the course of its traversal thereof for, if any substantial fraction of the energy is permitted to reach the end of the groove, it will be reflected backward so as to cause undesirable interference with the radiation of energy through the side of the groove, and may tend adversely to affect the shape of the radiation pattern.

While, as above indicated, the radiation pattern produced by the radiating element according to FIG. 2, may be relatively narrow in elevational width, it will generally be considerably broader in azimuthal width measured transversely with reference to the longitudinal axis of the groove, as is clearly shown, for a typical radiation pattern, in FIG. 2. In fact, the field strength of energy radiated from the groove may vary roughly cosinusoidally in azimuth on either side of a maximum directly opposite the open side of the groove. Thus the total azimuthal width of the pattern may be almost with the radiated field strength falling rapidly to zero in the vicinity of both boundaries of the beam.

I have found that, by virtue of this characteristic of the radiation pattern produced by a single element of the sort illustrated in FIG. 2, it is possible, by combining a plurality of such elements, each directed outward from a central axis, to produce an omnidirectional radiation pattern substantially of the sort discussed with reference to FIG. 1. For example, four radiating elements respectively designated 31, 32, 33 and 34 and each like the one illustrated in FIGv 2 may be disposed at equal intervals around the nose 35 of a missile in the manner shown in FIG. 3, and each may be supplied, through respective waveguide feeders 36, 37, 38 and 39, with microwave energy from a common source such as transceiver 40. In FIG. 3 the nose of the missile is shown in phantom to permit a clear showing of the arrangement within it of the antenna elements and their associated feeders. Additive combination of, and interference between the waves radiated by these four elements will result in their individual radiation patterns combining to yield a resultant azimuthal pattern comprised of a plurality of lobes, each narrower in azimuth than the individual radiation pattern of a single one of these elements. However, owing to the fact that the lobes in this resultant pattern are closely spaced and are all of substantially equal maximum field strength, they will provide virtually omnidirectional azimuthal coverage, as desired. It will be apparent that if the nose of the missile is constructed principally of some nonconductive material, then the elements of the form illustrated in FIG. 2 may simply be inserted in suitable recesses or openings in the surface, the outer edges of the conductive members, which define the sides of the grooves, being positioned flush with the surface, and they, together with the dielectric filling of the grooves, forming, in effect, a continuation of the surface, so that no discontinuities in the smooth surface will be presented to modify adversely the aerodynamic properties thereof. On the other hand, if the nose of the missile happens to be formed of a solid piece of metal, a radiating element equivalent to the one illustrated in FIG. 2 may be achieved simply by milling a groove of the appropriate dimensions in the surface of the nose and by machining a suitable channel to act as the feed for supplying electromagnetic wave energy to the groove. Such an arrangement, it will be apparent, is the substantial electrical equivalent of the structure shown in FIG. 2, and is within the contemplated scope of applicants invention.

Thus it will be seen that by my invention there is provided an exceedingly simple and versatile microwave energy radiating element for producing a radiation pattern, the characteristics of which are readily controllable by varying the parameters of the elements. By virtue of the manner in which the element is constructed it may readily be arranged in the surface of an aircraft, missile or projectile without adversely modifying the aerodynamic properties of such surface. The element may be used for both transmission and reception, and either alone or in combination with a plurality of other similar elements to produce a wide variety of different forms of radiation patterns. While the invention has been described with specific reference to use in conjunction with proximity fuse apparatus in a guided missile, it will be apparent that its use is in nowise so limited and that it may find application in numerous other instances, and particularly where the aerodynamic properties of a vehicle in which it may be mounted are an important consideration.

I claim:

1. In combination: a projectile having a nose portion with generally conical aerodynamic surface; a microwave antenna array situated in said nose portion and productive of a generally toroidal radiation pattern substantially coaxial with the longitudinal axis of said nose portion, said antenna array comprising a plurality of elongated grooves of substantially rectangular crosssection in said surface, said grooves lying substantially in planes common to said longitudinal axis of said nose portion and being spaced at intervals around said surface, each of said grooves being bounded by electrically conductive material; and means for feeding energy to said array through an aperture located at the bottom of each of said grooves and proximate one of the ends thereof.

2. In combination: an explosive projectile having a nose portion with generally conical aerodynamic surface and having an effective fragmentation pattern omnidirectional in azimuth about the longitudinal axis of said projectile including its nose portion and inclined in elevation in the direction of flight of said projectile; a microwave antenna array situated in said nose portion and conforming to said conical surface, said antenna array having a radiation pattern substantially coincident with said fragmentation pattern, said antenna array comprising a plurality of elongated grooves of substantially rectangular cross-section lying in said conical surface in planes common to said axis and spaced at equal azimuthal intervals circumferentially about said surface, each of said grooves being bounded by electrically conductive material and filled with solid dielectric material and each of said grooves extending into said nose portion to a depth of between A and /2 the wavelength of signals to be radiated therefrom; and means for supplying substantially identical microwave signals to said array through an aperture in the bottom and proximate the rearward end of each of said grooves.

3. In combination: a projectile having a nose portion with generally conical aerodynamic surface; a microwave antenna array situated in said nose portion and productive of a generally toroidal radiation pattern substantially coaxial with the longitudinal axis of said nose portion, said antenna array comprising four elongated grooves of substantially rectangular cross-section in said conical surface, said grooves lying substantially in planes common to said longitudinal axis and being spaced at substantially ninety degree intervals azimuthally around said surface, each of said grooves being bounded by electrically conductive material; and means for feeding energy to said array through an aperture located at the bottom of each of said grooves and proximate the rearward end thereof. 

1. In combination: a projectile having a nose portion with generally conical aerodynamic surface; a microwave antenna array situated in said nose portion and productive of a generally toroidal radiation pattern substantially coaxial with the longitudinal axis of said nose portion, said antenna array comprising a plurality of elongated grooves of substantially rectangular cross-section in said surface, said grooves lying substantially in planes common to said longitudinal axis of said nose portion and being spaced at intervals around said surface, each of said grooves being bounded by electrically conductive material; and means for feeding energy to said array through an aperture located at the bottom of each of said grooves and proximate one of the ends thereof.
 2. In combination: an explosive projectile having a nose portion with generally conical aerodynamic surface and having an effective fragmentation pattern omnidirectional in azimuth about the longitudinal axis of said projectile including its nose portion and inclined in elevation in the direction of flight of said projectile; a microwave antenna array situated in said nose portion and conforming to said conical surface, said antenna array having a radiation pattern substantially coincident with said fragmentation pattern, said antenna array comprising a plurality of elongated grooves of substantially rectangular cross-section lying in said conical surface in planes common to said axis and spaced at equal azimuthal intervals circumferentially about said surface, each of said grooves being bounded by electrically conductive material and filled with solid dielectric material and each of said grooves extending into said nose portion to a depth of between 1/4 and 1/2 the wavelength of signals to be radiated therefrom; and means for supplying substantially identical microwave signals to said array through an aperture in the bottom and proximate the rearward end of each of said grooves.
 3. In combination: a projectile having a nose portion with generally conical aerodynamic surface; a microwave antenna array situated in said nose portion and productive of a generally toroidal radiation pattern substantially coaxial with the longitudinal axis of said nose portion, said antenna array comprising four elongated grooves of substantially rectangular cross-section in said conical surface, said grooves lying substantially in planes common to said longitudinal axis and being spaced at substantially ninety degree intervals azimuthally around said surface, each of said grooves being bounded by electrically conductive material; and means for feeding energy to said array through an aperture located at the bottom of each of said grooves and proximate the rearward end thereof. 